The present invention relates to a system for measuring and/or checking the speed of an object, such as a vehicle or a boat, relative to a reference point.
The background of the invention is the need for a reliable system for surveying, e.g., the speed of vehicles moving on a road having a regulated speed limit. At present such surveillance is generally accomplished by means of various types of radar apparatus for speed measurement, such apparatus being placed close to the roadway. When the emitted radiation is reflected against a moving vehicle, an alteration in the frequency of the radiation (Doppler effect) occurs, and this frequency shift is proportional to the speed of the object. By registration on a strip of paper, a diagram is obtained, from which the vehicle speed may be determined.
However, this known method has several disadvantages, including the uncertainty of the measured values and the problems of subsequently analyzing the traffic situation at the time of measurement and positively identifying the vehicle.
Apart from such well-known speed measurement systems, a general traffic surveillance and control system using a TV-camera and video signal processing means is known from U.S. Pat. No. 3,685,012 of Aug. 15, 1972. Although the latter system can be used for determining a plurality of data relating to the traffic situation on a roadway, it is not ideally suited for speed measurement and supervision. Thus, the system comprises alternating patterns disposed on the surface of the roadway, and the TV-camera is mounted so that passing vehicles will partially obscure contrasting portions of the pattern in the field of view of the camera. The video signal is then processed to obtain various data associated with the vehicular traffic. However, the pattern to be placed on the road surface renders the system unsuitable for movable applications, e.g., for checking vehicle speeds at different locations along roads having speed regulations. Apart from the work involved in placing such pattern strips on the road surface, the patterns will be visible to the drivers of the vehicles, which makes secret surveillace impossible. Moreover, in winter, falling snow may totally cover the pattern and make measurements impossible.